Triaxial cables have been used for carrying electrical signals between detectors and monitoring instruments for some time. Many industries utilize triaxial cables for carrying signals from detectors to monitoring instruments. The nuclear power industry particularly uses triaxial cables to transmit various types of signals from detectors placed in and around a nuclear reactor to instruments which may be located some distance away from the detectors.
Generally, triaxial cables are comprised of three sheathed conductors. A center conductor carries electric current to the monitoring instrument corresponding to an electrical signal from a detector. A second conductor, generally denoted as an "inner shield," functions as return conductor for the electric current in the center conductor. An outer conductor functions as an outer conducting shield and prevents stray electromagnetic signals from impinging on the two inner conductors of the triaxial cable. Insulating layers are usually placed between the three conductors in the triaxial cable to electrically separate the conductors from one another.
Triaxial cables utilized in the nuclear power industry between detectors and monitoring units can carry voltages of up to about 2500 volts DC or small current signals in a range of about 10 picoamps to about 1 milliamp. Additionally, small pulse signals from neutron counters in a range from about 1 millivolt to about 10 millivolts may be carried on triaxial cables used in nuclear power monitoring equipment.
There are many types of triaxial cables which may be utilized to carry signals from detectors to monitoring equipment. Examples of such cables are the RG-11 triaxial cable, the RG-58 triaxial cable, and the RG-59 triaxial cable. The most common triaxial cable used in the nuclear power industry is the RG-11 triaxial cable which ensures minimal attenuation of detector signals and minimum interference of detector signals as they are transmitted over the cable to the monitoring instrument.
Termination of the RG-11 cable is usually within an instrument cabinet where the cable is connected to the instrument through a male or female RG-11/u connector. The physical construction of an RG-11 triaxial cable precludes bending it in any arc with a bend radius of less than 6 inches. If less than a 6-inch bend radius is encountered, the center conductor of the RG-11 cable may migrate through the insulation and voltage arcing between the inner conductors may occur, or shorts may develop with a concomitant loss of signal as a result. However, there is usually an insufficient area to maintain more than a 6-inch bend radius between the rear cabinet door and the instrument and therefore for instruments which use RG-11 cables, the rear cabinet doors are usually left open to prevent the RG-11 cable from being forced into a bend radius of less than 6 inches.
Today, the Nuclear Regulatory Commission enforces closing of the instrument cabinet doors to ensure safety. Thus, there is a need in the art for a practical solution for using existing RG-11 triaxial cables with nuclear monitoring instrumentation having RG-11 instrument bulkhead connectors while complying with federal regulations. Replacement of the RG-11 triaxial cables and associated instrument bulkhead connectors is not practical since the associated downtime, costs, testing and calibration times are all too high. A possible solution is to interpose a smaller, more flexible triaxial cable having a smaller bend radius between the termination end of the RG-11 cable and the connector on the instrument while maintaining signal integrity through a splice of the two cables and associated connectors.
Potential triaxial cables are the RG-58 and RG-59 triaxial cables, both which have a bend radius of about 2-3 inches. However, heretofore no existing connector adapter has been produced or designed for connecting different sized triaxial cables together. Furthermore, it is not practical to change from triaxial cables to coaxial cables using a coaxial connector adapter since loss of the outer shield found in a triaxial cable when a coaxial cable is used creates a substantial opportunity for introducing signal interference and noise during monitoring of a particular process in a nuclear power plant.
There is therefore a long-felt need in the art for a triaxial connector adapter which interfaces RG-11 to RG-58, RG-11 to RG-59, and RG-11 to RG-11 triaxial cables while maintaining total signal integrity and isolation through the connector adapter. Furthermore, triaxial connector adapters should permit changing the mating interface of BNC, TNC or RG-59 triaxial connectors.